1. Field of the Invention
The present invention relates generally to a multi-point probe assembly for testing electronic devices such as an integrated circuit, a flat panel display or the like. More specifically, the present invention relates to a multi-point probe assembly which is easy to assemble with the contact pressure variations between probe arms maintained essentially uniform and (b) this essentially uniform contact pressure can be retained even after the long use of the assembly.
2. Description of the Prior Art
Various types of multi-point test probe assemblies have been developed hitherto for testing electronic devices of the above mentioned type. One example of such a device is disclosed in Japanese Patent Publication No. 54-43354 (corresponding to U.S. application Ser. No. 799,472 filed Feb. 14, 1969).
This prior art test probe assembly, illustrated in FIGS. 1 and 2, is equipped with a plurality of needle-like probe arms or probe pins 2. It should be noted that throughout the instant specification each of the term "probe arm" and "pin" has an identical meaning. Each of these arms 2 has a radially outboard end portion, and an intermediate portion which is supported by a combination of a circularly shaped supporting member 4 and a circularly shaped holding member 5 positioned on one of two main surfaces of the printed board 1. The holding member 5 is formed of an insulating, thermosetting material. As shown in FIG. 1, the probe arms 2 are arranged in an essentially conical formation and at predetermined angular intervals with respect to the center of the printed board 1.
The radially outer end portions of the probe arms 2 are connected to printed lines 6 formed on one surface of the printed board 1 by means of soldering (7). These printed lines 6 extend into through-holes 8 and are connected with pins (terminals) (not shown) of an external electronic-device test system, which are received therein.
The inboard end portions of the probe arms 2 protrude into the space formed inside the holding member 5 in a manner such that probe-points 3 formed at the inboard ends of the probe arms are accurately positioned on a given plane below the lower surface of the holding member 5.
During testing of an electronic device (not shown), the probe points 3 are respectively brought into contact with terminals of the electronic device in a manner which establishes electrical connections with the device under test.
However, this arrangement has suffered from the drawback that the contact pressure with which the probe points 3 are brought into contact with the terminals of the device under test, is not uniform. The reason for this is that the lengths of the probe arms differ due to the radial arrangement of the same.
Further, the Young's modulus of the thermosetting material (e.g. epoxy resin) from which the holding member 5 is formed, is small as compared with that of the probe arm. Therefore, it is very difficult that the holding member 5 fixedly holds the very small deviations of the probe arm 2. It follows that, depending on the amount of contact pressure which is applied, the probe arm 2 is undersirably allowed to be slightly deviated. In such an instance, the point at which each of the probe arms is actually supported, moves toward the soldered point 7. As a result, depending on the amount of overdrive of each of the probe arms 2, the initially arranged position of each of the probe points 3 tends to deviate as the assembly is used or with the passing of time. This accentuates the problem that the contact pressure between the probe arms 2 is not uniform.
Still further, in the case of the arrangement shown in FIGS. 1 and 2, the probe arms 2 are not subject to any downwardly acting bias. Therefore, in order to achieve a relatively good level of contact pressure, it is necessary to increase the strength of the probe arm by either increasing the diameter of the same or using a hard, relatively expensive material such as Tungsten or the like. However, increasing the thickness or diameter of the probe arm inherently limits the pitch at which the probe arms can be arranged.